The present invention relates to a rotary developing device incorporated in image forming equipment and having a plurality of developing units rotatably mounted on a rotary shaft and rotating the developing units for sequentially developing latent images electrostatically formed on an image carrier at a developing position where the developing units sequentially face the image carrier.
One of conventional image forming equipment exposes a photoconductive element or similar image carrier by imagewise light undergone color separation to electrostatically form latent images, develops each of the latent images by a toner of particular color complementary to the imagewise light, and transfers the resulting toner images one above another to a single paper sheet. Another conventional image forming equipment electrostatically forms latent images of a single image which should be rendered in different colors on respective image carriers, develops the latent images by toners of different colors, and transfers the resulting toner images one above another to a single paper sheet. Such image forming equipment, whether it be of the first-mentioned type or of the second mentioned type, needs a plurality of developing units, i.e., a plurality of developing units should be constructed independently of one another and juxtaposed in the vicinity of the image carrier, resulting in a bulky construction.
To eliminate the above problem, a rotary developing device having a plurality of developing units rotatably mounted on a rotary shaft has been proposed. This type of developing device rotates the developing units for sequentially developing latent images electrostatically formed on an image carrier at a developing position where the developing units sequentially face the image carrier. For example, Japanese Patent Laid-Open Publication No. 172660/1983 discloses a developing device having partitions extending radially away from a rotary shaft to divide the space between two side plates of the device into a plurality of developing chambers. Japanese Patent Laid-Open Publication No. 73163/1986 teaches a developing device having a plurality of developing units which are removably mounted on a common support body having a center shaft. These conventional developing devices, however, have various problems left unsolved, as follows.
The developing device taught in the first-mentioned Laid-Open Publication has developing rollers and other components of the developing units mounted on the side plates of the device independently of one another. This not only makes it difficult to assemble the components but also complicates the replacement of the developing rollers and blades which regulate the thickness of developer layers deposited on the developing rollers. Moreover, the position or the distance of each developing roller from the image carrier or the rotary shaft or the contact pressure exerted by the former on the latter is determined solely by the accuracy of parts constituting the side plates of the device. Therefore, once the distance, for example, between any developing roller and the image carrier is deviated from predetermined one, the image density will become insufficient or become irregular in the lengthwise direction of the roller. In this manner, since each developing roller, for example, cannot be adjusted in position relative to the image carrier, the parts and elements constituting the developing device should be machined with utmost accuracy and are, therefore, expensive.
On the other hand, the developing device disclosed in the second-mentioned Laid-Open Publication allows the distance, for example, between each developing roller and the image carrier to be adjusted since the developing units are provided independently of one another. However, such a developing device is more bulky and heavier than the developing device of the first-mentioned Laid-Open Publication and needs a greater number of parts, again resulting in an expensive construction. In addition, when only the position of any developing unit is adjusted, a gear train for transmitting a driving force to the developing unit is brought out of accurate meshing.